[Perl/perl5] bc6e83: Suppress -Wunused_variable warning during 'make'

[James E Keenan via perl5-changes]

  Branch: refs/heads/smoke-me/jkeenan/gh-21293-unused-var
  Home:   https://github.com/Perl/perl5
  Commit: bc6e83cef73b32e723480519dd4fae9d43b46be5
      
https://github.com/Perl/perl5/commit/bc6e83cef73b32e723480519dd4fae9d43b46be5
  Author: James E Keenan <jkee...@cpan.org>
  Date:   2023-08-21 (Mon, 21 Aug 2023)

  Changed paths:
    M pp_ctl.c

  Log Message:
  -----------
  Suppress -Wunused_variable warning during 'make'

Implement Dave Mitchell's suggestion: we don't really need the unused
variable.

For: https://github.com/Perl/perl5/issues/21393